In medicine, a natural conduit in a body may be locally flow constricted or damaged. A stent or stent graft may be inserted into this natural conduit, in order to counteract such a flow constriction or to repair damage. Stents may be deployed by means of a balloon catheter. The stent is crimped around the balloon before deployment, the catheter is introduced into a body lumen and once the balloon is positioned appropriately, the balloon is inflated and expands the stent.
FIGS. 1a to 1d illustrate a few exemplary chronologic steps of inflating a balloon from the state of the art. The balloon shown in these Figures is used for deploying a stent which is crimped around the balloon. FIG. 1a shows the unexpanded state of the balloon and stent. As shown in FIG. 1b, when starting to introduce pressure into the balloon, its expansion begins at the outer ends. This phenomena is called dog boning and is caused by the resistance for expanding this part being smaller than in the center of the balloon/stent assembly (the struts in the middle are held in position from both sides, whereas at the end struts are only held from one side). From there, the expansion of the balloon/stent proceeds towards a center of the balloon/stent until the entire balloon is expanded, as shown in FIG. 1d. The dog-boning of the balloon cones has a so-called foreshortening effect for the stent, which means that the stent is shortened longitudinally to a small extend. This foreshortening effect is undesirable, because it makes the expanded length deviate from the unexpanded length.
FIG. 2 schematically shows a typical diagram of the relationship between the pressure inside a balloon and its diameter. As illustrated, the pressure inside the balloon increases up to a nominal pressure 1, at which the balloon is considered to be fully expanded. If the pressure is increased further, the balloon diameter does not increase substantially any more. When exceeding a burst pressure 2, the balloon may burst.